1. Field of the Invention
The present invention relates generally to drawstrings for removal of stents and, more particularly, to a drawstring for removal of a stent which is configured such that when the drawstring is pulled by a stent removal device to remove the stent from a lumen, for example, to conduct reoperation, the stent is extended in a longitudinal direction and contracted in diameter by the drawstring, so that the stent which has been grasped by the inner wall of the lumen can be easily separated therefrom, thus facilitating the removal of the stent.
2. Description of the Related Art
Generally, a medical stent is used to expand a lumen which has contracted in diameter or to prevent expanded lumens from contracting.
In other words, medical stents functions to expand a lumen which has contracted, for example, by the occurrence of a tumor such as cancer, or to prevent the progression of contraction of a lumen.
For instance, such a medical stent is used to cope with the contraction of a pancreatic duct because of acute pancreatitis, the contraction of a bile duct attributable to chronic cholangitis, the temporary contraction of a lumen occurring after surgery, etc. Particularly, the medical stent which has been used to prevent symptoms of the temporary contraction of a lumen or to expand a contracted lumen is removed from the lumen after the lumen has recovered its original state. In addition, when the stent is placed in the lumen at an incorrect position and thus does not function as normal or is rendered ineffectual, the stent which has been placed in the lumen must be removed therefrom before reoperation can be conducted.
Typically, the stent which can be removed is inserted into a lumen by a well-known catheter to prevent contraction of the lumen or expand the diameter of the lumen. When the stent is removed from the lumen, if a leading and of the stent with respect to the direction in which the stent is extracted can be contracted in diameter, the removal of the stent is facilitated.
Preferably, the stent is configured such that it can be removed from the lumen using a hook of a stent removal device. With regard to the structure for removal of the stent, a plurality of loops is integrally connected to a stent body and to a cover which covers the inner and outer surfaces of the stent body. In addition, at least one string is connected at both ends thereof to each loop.
Therefore, to remove the stent from the lumen, the hook is inserted into the stent body and moved forwards and backwards until it becomes hooked to one loop. Thereafter, the hook is pulled. Then, the stent contracts towards the central axis thereof.
When the hook is further pulled, the stent body is inserted into a tube of the stent removal device. Subsequently, the stent is completely removed from the lumen by removing the tube and the hook from the lumen together.
As shown in FIGS. 1 and 2, in the conventional stent having the above-mentioned structure, the stent is extracted from the lumen in such a way that the hook is hooked to one of the loops and pulled. However, when the stent is pulled by the hook, the pulling force is concentrated on only a portion of the circumference of the stent. Thereby, although the stent is extended in length, a ratio of reduction in the diameter of the stent is relatively low, thus making the extraction of the stent from the lumen difficult.
Furthermore, when the stent remains in the lumen for a long period of time, a lesion portion or lumen tissue may become stuck or attached to the stent. In this case, the stent is not easily extracted from the lumen by the pulling force. Rather, the lesion portion or lumen tissue is pulled along with the stent, thus resulting in the recurrence of a lesion or pain to a patient.
In addition, regardless of an area of the lesion portion, the loops are provided only on the end of the stent. Hence, when one of the loops is pulled, the pulling force is concentrated on the end of the stent but may not be transmitted to the portion of the stent to which the lesion portion is stuck or attached, so that the removal of the stent becomes difficult.
Therefore, a drawstring for removal of a stent is required, which is configured such that when a loop is pulled, the pulling force is transmitted to the entire stent and simultaneously the diameter of the stent is reduced so that the stent can be easily removed from a lumen, even when it is in a state of being grasped by the inner wall of the lumen.